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Prebiotic synthesis of amino acids, nucleobases, lipids, and other building blocks of protocells and metabolisms is still poorly understood. Proposed reactions that produce individual components such as the Strecker synthesis of amino acids, the formose reaction for the production of sugars, and prebiotic syntheses for the production of nucleobases. These syntheses often rely on different starting reagents, different conditions (temperature, pH, catalysts, etc.), and often will interfere with each other. These challenges have made determining the conditions for the origin of life difficult. Researchers have turned to systems chemistry type approaches to help overcome some of these challenges. Systems chemistry approaches form multiple products form a single synthesis under the same conditions and tend to be more similar to biological processes in that they have emergent properties, self-organization, and autocatalysis. Cyanosulfidic prebiotic synthesis is a systems chemistry approach. | 9 | Geochemistry |
Amalgamation with mercury can be used to recover very small gold particles, and mercury is still widely used in small-scale artisanal mining across the world. Mercury forms a mercury-gold amalgam with smaller gold particles, and then the gold is concentrated by boiling away the mercury from the amalgam. This is effective in extracting very small gold particles, but the process is hazardous due to the toxicity of mercury vapour. Large-scale use of mercury stopped in the 1960s. However, mercury is still used in artisanal and small-scale gold mining (ASGM). One mechanism by which mercury is employed in hydraulic mining is as an "undercurrent", in which the flow of smaller grains is diverted over mercury-coated copper plates. High flow velocities associated with hydraulic mining cause flouring of mercury, the wearing down of mercury particles that contributes to mercury loss into the environment.
Over of mercury contaminated the environment in California as a result of placer mining in the late nineteenth and early twentieth centuries. Stamp mill mining contributed an additional of mercury contamination. Mercury contamination in California waterways is a major contemporary environmental issue, as is groundwater pollution, mostly by inorganic mercury. | 8 | Metallurgy |
Sevoflurane will degrade into what is most commonly referred to as compound A (fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether) when in contact with CO absorbents, and this degradation tends to enhance with decreased fresh gas flow rates, increased temperatures, and increased sevoflurane concentration. Compound A is what some believe is in correlation with renal damage. | 2 | Environmental Chemistry |
The development started with early work on the underlying sensor technology. One of the first portable, chemistry-based sensors was the glass pH electrode, invented in 1922 by Hughes. The basic concept of using exchange sites to create permselective membranes was used to develop other ion sensors in subsequent years. For example, a K sensor was produced by incorporating valinomycin into a thin membrane.
In 1953, Watson and Crick announced their discovery of the now familiar double helix structure of DNA molecules and set the stage for genetics research that continues to the present day. The development of sequencing techniques in 1977 by Gilbert and Sanger (working separately) enabled researchers to directly read the genetic codes that provide instructions for protein synthesis. This research showed how hybridization of complementary single oligonucleotide strands could be used as a basis for DNA sensing. Two additional developments enabled the technology used in modern DNA-based. First, in 1983 Kary Mullis invented the polymerase chain reaction (PCR) technique, a method for amplifying DNA concentrations. This discovery made possible the detection of extremely small quantities of DNA in samples. Secondly in 1986 Hood and co-workers devised a method to label DNA molecules with fluorescent tags instead of radiolabels, thus enabling hybridization experiments to be observed optically.
Figure 1 shows the make up of a typical biochip platform. The actual sensing component (or "chip") is just one piece of a complete analysis system. Transduction must be done to translate the actual sensing event (DNA binding, oxidation/reduction, etc.) into a format understandable by a computer (voltage, light intensity, mass, etc.), which then enables additional analysis and processing to produce a final, human-readable output. The multiple technologies needed to make a successful biochip—from sensing chemistry, to microarraying, to signal processing—require a true multidisciplinary approach, making the barrier to entry steep. One of the first commercial biochips was introduced by Affymetrix. Their "GeneChip" products contain thousands of individual DNA sensors for use in sensing defects, or single nucleotide polymorphisms (SNPs), in genes such as p53 (a tumor suppressor) and BRCA1 and BRCA2 (related to breast cancer). The chips are produced by using microlithography techniques traditionally used to fabricate integrated circuits (see below). | 1 | Biochemistry |
Stercobilin is a tetrapyrrolic bile pigment and is one end-product of heme catabolism. It is the chemical responsible for the brown color of human feces and was originally isolated from feces in 1932. Stercobilin (and related urobilin) can be used as a marker for biochemical identification of fecal pollution levels in rivers. | 1 | Biochemistry |
ArcB is a membrane-bound sensor histidine kinase. It is unusual in that it contains three distinct signaling domains. It senses oxygen levels in the cell by interacting with reduced quinone. When reduced quinone levels are high, it signals that the cell is engaged in aerobic respiration. When reduced quinone levels are low, it signals that the cells is unable to perform aerobic respiration. This is typically due to insufficient levels of oxygen, which acts as the terminal electron receptor in the electron transport chain. ArcB is then able to activate or deactivate ArcA, the response regulator, which can then travel to the chromosome and regulate gene expression.
ArcA is activated via phosphorylation. When oxygen is present in the cell ArcB autophosphorylates. This inorganic phosphate is then transferred via a four amino acid phosphorelay to ArcA. Phosphorylated ArcA is then able to attach to specific, consensus gene sequences on the chromosome regulating approximately 30 different operons. ArcA is able to acts as both a repressor and an activator depending on which operon it attaches.
When oxygen levels are low, ArcB acts as a phosphatase, removing the inorganic phosphate group from ArcA. Without the attached phosphate group, ArcA is unable to bind to DNA and genes return to their original, aerobic levels of expression. This allows the cell to engage in metabolic pathways that are most advantageous for the current conditons of the cell. Dephosphorylation utilizes the same phosphorelay as phosphorylation, but it is operated in reverse.
Without the Arc system being present throughout various strains of anaerobic bacteria, gene expression could not efficiently control the metabolism during the replication of genetic material. Under many growth conditions where oxygen is not present, the ArcB sensor kinase (which is membrane-bound) turns to autophosphorylates which is a process proven to be more efficient when certain fermenting metabolites such as Pyruvate, Acetate, and D-Lactate. | 1 | Biochemistry |
*ADRBK1 can downregulate response to epinephrine
*AGPAT1 acyl 3 phosphoglycerol acyl transferase
*ARF1
*ARF3
*ARF4
*ARF5
*ARL2 RAS Superfamily
*CSF1 Colony stimulating factor not highly expressed constitutively at 5-12
*CSK C-src tyrosine kinase
*DCT dopachrome tautomerase
*EFNA3
*FKBP1A
*GDI1 GDP Dissociation inhibitor (Rab family)
*GNAS1 ubiquitously expressed, but differentially imprinted
*GNAI2
*HAX1 associated with tyrosine kinases
*ILK Integrin linked kinase
*MAPKAPK2
*MAP2K2
*MAP3K11
*PITPNM Phosphatidylinositol transfer protein
*RAC1 Ro GTPase involved with many signaling pathways
*RAP1B GTPase involved with cell adhesion
*RAGA Ras-related GTP Binding
*STK19
*STK24 Serine/Threonine Kinase
*STK25
*YWHAB Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, beta polypeptide
*YWHAH Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, h polypeptide
*YWHAQ Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, theta polypeptide
*YWHAZ Tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, zeta polypeptide | 1 | Biochemistry |
Succinyl coenzyme A synthetase (SCS, also known as succinyl-CoA synthetase or succinate thiokinase or succinate-CoA ligase) is an enzyme that catalyzes the reversible reaction of succinyl-CoA to succinate. The enzyme facilitates the coupling of this reaction to the formation of a nucleoside triphosphate molecule (either GTP or ATP) from an inorganic phosphate molecule and a nucleoside diphosphate molecule (either GDP or ADP). It plays a key role as one of the catalysts involved in the citric acid cycle, a central pathway in cellular metabolism, and it is located within the mitochondrial matrix of a cell. | 1 | Biochemistry |
Various cellular reactions to ultrasound indicate the mechanism of molecular uptake via endocytosis. These observed reactionary phenomena include ion exchange, hydrogen peroxide, and cell intracellular calcium concentration. Studies have used patch clamping techniques to monitor membrane potential ion exchange for the role of endocytosis in sonoporation. Ultrasound application to cells and adjacent microbubbles was shown to produce marked cell membrane hyperpolarization along with progressive intracellular calcium increase, which is believed to be a consequence of calcium channels opening in response to microbubble oscillations. These findings act as support for ultrasound application inducing calcium-mediated uncoating of clathrin-coated pits seen in traditional endocytosis pathways. Other work reported sonoporation induced the formation of hydrogen peroxide, a cellular reaction that is also known to be involved with endocytosis. | 1 | Biochemistry |
Crystals can be classified in three ways: lattice systems, crystal systems and crystal families. The various classifications are often confused: in particular the trigonal crystal system is often confused with the rhombohedral lattice system, and the term "crystal system" is sometimes used to mean "lattice system" or "crystal family". | 3 | Analytical Chemistry |
Compounds such as 2,2,2-trichloroethanol, which contain multiple geminal halogens adjacent to a hydroxyl group may be considered halohydrins (although, strictly speaking, they fail the IUPAC definition) as they possess similar chemistry. In particular they also undergo intramolecular cyclisation to form dihaloepoxy groups. These species are both highly reactive and synthetically useful, forming the basis of the Jocic–Reeve reaction, Bargellini reaction and Corey–Link reaction. | 0 | Organic Chemistry |
A Mössbauer spectrograph was made of the dust that gathered on Opportunity's capture magnet. The results suggested that the magnetic component of the dust was titanomagnetite, rather than just plain magnetite, as was once thought. A small amount of olivine was also detected which was interpreted as indicating a long arid period on the planet. On the other hand, a small amount of hematite that was present meant that there may have been liquid water for a short time in the early history of the planet.
Because the Rock Abrasion Tool (RAT) found it easy to grind into the bedrocks, it is thought that the rocks are much softer than the rocks at Gusev crater. | 9 | Geochemistry |
The pipecolate region of rapamycin structure seems necessary for rapamycin-binding to FKBP12. This step is required for further binding of rapamycin to the mTOR kinase, which is the key enzyme in many biological actions of rapamycin.
The high affinity of rapamycin binding to FKBP12 is explained by number of hydrogen bonds through two different hydrophobic binding pockets, and this has been revealed by X-ray crystal structure of the compound bound to the protein. The structural characteristics common to temsirolimus and sirolimus; the pipecolic acid, tricarbonyl region from C13-C15, and lactone functionalities play the key role in binding groups with the FKBP12.
The most important hydrogen bonds are the lactone carbonyl oxygen at C-21 to the backbone NH of Ile56, amide carbonyl at C-15 to the phenolic group on the sidechain of Tyr82, and the hydroxyl proton at the hemiketal carbon, C-13, to the sidechain of Asp37.
Structural changes to the rapamycin structure can affect binding to mTOR. This could include both direct and indirect binding as a part of binding to FKBP12. Interaction of the FKBP12-rapamycin complex with mTOR corresponds with conformational flexibility of the effector domain of rapamycin. This domain consists of molecular regions that make hydrophobic interactions with the FKB domain and triene region from C-1-C-6, methoxy group at C-7, and methyl groups at C-33, C-27 and C-25. All changes of the macrolide ring can have unpredictable effects on binding and therefore, make determination of SAR for rapalogs problematic.
Rapamycin contains no functional groups that ionize in the pH range 1-10 and therefore, are rather insoluble in water. Despite its effectiveness in preclinic cancer models, its poor solubility in water, stability, and the long half-life elimination made its parenteral use difficult, but the development of soluble rapamycin analogs vanquished various barriers.
Nonetheless, the rapamycin analogs that have been approved for human use are modified at C-43 hydroxyl group and show improvement in pharmacokinetic parameters as well as drug properties, for example, solubility.
Rapamycin and temsirolimus have similar chemical structures and bind to FKBP12, though their mechanism of action differs.
Temsirolimus is a dihydroxymethyl propionic acid ester of rapamycin, and its first derivative. Therefore, it is more water-soluble, and due to its water solubility it can be given by intravenous formulation.
Everolimus has O-2 hydroxyethyl chain substitution and deforolimus has a phosphine oxide substitution at position C-43 in the lactone ring of rapamycin.
Deforolimus (Ridaforolimus ) has C43 secondary alcohol moiety of the cyclohexyl group of Rapamycin that was substituted with phosphonate and phosphinate groups, preventing the high-affinity binding to mTOR and FKBP. Computational modelling studies helped the synthesise of the compound. | 1 | Biochemistry |
For a spherical particle the surface area will scale as the square of the size, while the volume scales as the cube. Therefore surface contributions to the energy can become important at small sizes in nanoparticles. If the energy of the surface atoms is lower when they are closer, this can be accomplished by shrinking the whole particle. The gain in energy from the surface stress will scale as the area, balanced by an energy cost for the shrinking (deformation) that scales as the volume. Combined these lead to a change in the lattice parameter that scales inversely with size. This has been measured for many materials using either electron diffraction or x-ray diffraction. This phenomenon has sometimes been written as equivalent to the Laplace pressure, also called the capillary pressure, in both cases with a surface tension. This is not correct since these are terms that apply to liquids.
One complication is that the changes in lattice parameter lead to more involved forms for nanoparticles with more complex shapes or when surface segregation can occur. | 7 | Physical Chemistry |
Site energy is the term used in North America for the amount of end-use energy of all forms consumed at a specified location. This can be a mix of primary energy (such as natural gas burned at the site) and secondary energy (such as electricity). Site energy is measured at the campus, building, or sub-building level and is the basis for energy charges on utility bills.
Source energy, in contrast, is the term used in North America for the amount of primary energy consumed in order to provide a facility’s site energy. It is always greater than the site energy, as it includes all site energy and adds to it the energy lost during transmission, delivery, and conversion. While source or primary energy provides a more complete picture of energy consumption, it cannot be measured directly and must be calculated using conversion factors from site energy measurements. For electricity, a typical value is three units of source energy for one unit of site energy. However, this can vary considerably depending on factors such as the primary energy source or fuel type, the type of power plant, and the transmission infrastructure. One full set of conversion factors is available as technical reference from Energy STAR.
Either site or source energy can be an appropriate metric when comparing or analyzing energy use of different facilities. The U.S Energy Information Administration, for example, uses primary (source) energy for its energy overviews but site energy for its Commercial Building Energy Consumption Survey and Residential Building Energy Consumption Survey. The US Environmental Protection Agency's Energy STAR program recommends using source energy, and the US Department of Energy uses site energy in its definition of a zero net energy building. | 7 | Physical Chemistry |
Low-energy surfaces primarily interact with liquids through dispersive (van der Waals) forces. William Zisman produced several key findings:
Zisman observed that cos θ increases linearly as the surface tension (γ) of the liquid decreased. Thus, he was able to establish a linear function between cos θ and the surface tension (γ) for various organic liquids.
A surface is more wettable when γ and θ is low. Zisman termed the intercept of these lines when cos θ = 1 as the critical surface tension (γ) of that surface. This critical surface tension is an important parameter because it is a characteristic of only the solid.
Knowing the critical surface tension of a solid, it is possible to predict the wettability of the surface.
The wettability of a surface is determined by the outermost chemical groups of the solid.
Differences in wettability between surfaces that are similar in structure are due to differences in the packing of the atoms. For instance, if a surface has branched chains, it will have poorer packing than a surface with straight chains.
Lower critical surface tension means a less wettable material surface. | 7 | Physical Chemistry |
Methylation sometimes involve use of nucleophilic methyl reagents. Strongly nucleophilic methylating agents include methyllithium () or Grignard reagents such as methylmagnesium bromide (). For example, will add methyl groups to the carbonyl (C=O) of ketones and aldehyde.:
Milder methylating agents include tetramethyltin, dimethylzinc, and trimethylaluminium. | 0 | Organic Chemistry |
Several advantages in both spatial resolution and minimizing photodamage/photobleaching in organic and/or biological samples are obtained by two-photon or three-photon excitation FCS. | 7 | Physical Chemistry |
Acetone is fragmented in two different groups, one carbonyl group and two methyl groups. For the critical volume the following calculation results:
V = 40 + 60.0 + 2 * 55.0 = 210 cm
In the literature (such as in the Dortmund Data Bank) the values 215.90 cm, 230.5 cm and 209.0 cm are published. | 7 | Physical Chemistry |
Plant viruses can be used to engineer viral vectors, tools commonly used by molecular biologists to deliver genetic material into plant cells; they are also sources of biomaterials and nanotechnology devices. Knowledge of plant viruses and their components has been instrumental for the development of modern plant biotechnology. The use of plant viruses to enhance the beauty of ornamental plants can be considered the first recorded application of plant viruses. Tulip breaking virus is famous for its dramatic effects on the color of the tulip perianth, an effect highly sought after during the 17th-century Dutch "tulip mania." Tobacco mosaic virus (TMV) and cauliflower mosaic virus (CaMV) are frequently used in plant molecular biology. Of special interest is the CaMV 35S promoter, which is a very strong promoter most frequently used in plant transformations. Viral vectors based on tobacco mosaic virus include those of the [https://www.icongenetics.com/technology/ magnICON®] and TRBO plant expression technologies.
Representative applications of plant viruses are listed below. | 1 | Biochemistry |
Ohta sought to order energy form conversions according to their quality and introduced a hierarchical scale for ranking energy quality based on the relative ease of energy conversion (see table to right after Ohta, p. 90). It is evident that Ohta did not analyse all forms of energy. For example, water is left out of his evaluation. It is important to note that the ranking of energy quality is not determined solely with reference to the efficiency of the energy conversion. This is to say that the evaluation of "relative ease" of an energy conversion is only partly dependent on transformation efficiency. As Ohta wrote, "the turbine generator and the electric motor have nearly the same efficiency, therefore we cannot say which has the higher quality" (1994, p. 90). Ohta therefore also included, abundance in nature as another criterion for the determination energy quality rank. For example, Ohta said that, "the only electrical energy which exists in natural circumstances is lightning, while many mechanical energies exist." (Ibid.). (See also table 1. in [http://www.exergy.se/ftp/japan85.pdf Wall's article] for another example ranking of energy quality). | 7 | Physical Chemistry |
Molecular analysis based on 16S rRNA sequences shows GFAJ-1 to be closely related to other moderate halophile ("salt-loving") bacteria of the family Halomonadaceae. Although the authors produced a cladogram in which the strain is nested among members of Halomonas, including H. alkaliphila and H. venusta, they did not explicitly assign the strain to that genus. Many bacteria are known to be able to tolerate high levels of arsenic, and to have a proclivity to take it up into their cells. However, GFAJ-1 was controversially proposed to go a step further; when starved of phosphorus, it was proposed to instead incorporate arsenic into its metabolites and macromolecules and continue growing.
The sequence of the genome of the bacterium GFAJ-1 is now posted in GenBank. | 1 | Biochemistry |
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File:Bifacial leaf cross section.jpg|Cross-section of a leaf
File:Leaf epidermis 2.jpg|Epidermal cells
File:Leaf spongy mesophyll.jpg|Spongy mesophyll cells | 5 | Photochemistry |
SCS is the only enzyme in the citric acid cycle that catalyzes a reaction in which a nucleotide triphosphate (GTP or ATP) is formed by substrate-level phosphorylation. Research studies have shown that E. coli SCSs can catalyze either GTP or ATP formation. However, mammals possess different types of SCSs that are specific for either GTP (G-SCS) or ATP (A-SCS) and are native to different types of tissue within the organism. An interesting study using pigeon cells showed that GTP specific SCSs were located in pigeon liver cells, and ATP specific SCSs were located in the pigeon breast muscle cells. Further research revealed a similar phenomenon of GTP and ATP specific SCSs in rat, mouse, and human tissue. It appears that tissue typically involved in anabolic metabolism (like the liver and kidneys) express G-SCS, whereas tissue involved in catabolic metabolism (like the brain, the heart, and muscular tissue) express A-SCS. | 1 | Biochemistry |
Certain species of hornwort are the only land plants which are known to have a biophysical CCM involving concentration of carbon dioxide within pyrenoids in their chloroplasts. | 5 | Photochemistry |
* When solute particles associate in solution, is less than 1. For example, carboxylic acids such as acetic acid (ethanoic acid) or benzoic acid form dimers in benzene, so that the number of solute particles is half the number of acid molecules.
* When solute particles dissociate in solution, is greater than 1 (e.g. sodium chloride in water, potassium chloride in water, magnesium chloride in water).
* When solute particles neither dissociate nor associate in solution, equals 1 (e.g. glucose in water).
The value of is the actual number of particles in solution after dissociation divided by the number of formula units initially dissolved in solution and means the number of particles per formula unit of the solute when a solution is dilute. | 7 | Physical Chemistry |
Landauer stated that information is physical. His principle sets fundamental thermodynamical constraints for classical and quantum information processing. Much effort has been dedicated to incorporating information into thermodynamics and measuring the entropic and energetic costs of manipulating information. Gaining information, decreases entropy which has an energy cost. This energy has to be collected from the environment. Landauer established equivalence of one bit of information with entropy which is represented by kT ln 2, where k is the Boltzmann constant and T is room temperature. This bound is called the Landauers limit. Erasing energy increases entropy instead. Toyabe et al. (2010) were able to demonstrate experimentally that information can be converted in free energy. It is a quite elegant experiment that consists of a microscopic particle on a spiral-staircase-like potential. The step has a height corresponding to kT, where k is the Boltzmann constant and T is the temperature. The particle jumps between steps due to random thermal motions. Since the downward jumps following the gradient are more frequent than the upward ones, the particle falls down the stairs, on average. But when an upward jump is observed, a block is placed behind the particle to prevent it from falling, just like in a ratchet. This way it should climb the stairs. Information is gained by measuring the particles location, which is equivalent to a gain in energy, i.e. a decrease in entropy. They used a generalized equation for the second law that contains a variable for information:
ΔF is the free energy between states, W is the work done on the system, k is the Boltzmann constant, T is temperature, and I is the mutual information content obtained by measurements. The brackets indicate that the energy is an average. They could convert the equivalent of one bit information to 0.28 of energy or, in other words, they could exploit more than a quarter of the information’s energy content. | 6 | Supramolecular Chemistry |
Primary minerals are the minerals that crystalize during the formation of Earths crust, and their typical δSi isotopic value is in the range of −0.9‰ – +1.4‰. Earths crust is constantly undergoing weathering processes, which dissolve Si and produce secondary Si minerals simultaneously. The formation of secondary Si discriminates against the heavy Si isotope (Si), creating minerals with relatively low δSi isotopic values (−3‰ – +2.5‰, mean: −1.1‰). It has been suggested that this isotopic fractionation is controlled by the kinetic isotope effect of Si adsorption to Aluminum hydroxides, which takes place in early stages of weathering. As a result of incorporation of lighter Si isotopes into secondary minerals, the remaining dissolved Si will be relative enriched in the heavy Si isotope (Si), and associated with relatively high δSi isotopic values (−1‰ – +2‰, mean: +0.8‰). The dissolved Si is often transported by rivers to the oceans. | 9 | Geochemistry |
Developing well-constructed models (accounting for variables such as oil type, salinity and surfactant) are necessary to select the appropriate dispersant in a given situation. Two models exist which integrate the use of dispersants: Mackays model and Johansens model. There are several parameters which must be considered when creating a dispersion model, including oil-slick thickness, advection, resurfacing and wave action. A general problem in modeling dispersants is that they change several of these parameters; surfactants lower the thickness of the film, increase the amount of diffusion into the water column and increase the amount of breakup caused by wave action. This causes the oil slick's behavior to be more dominated by vertical diffusion than horizontal advection.
One equation for the modeling of oil spills is:
where
* h is the oil-slick thickness
* is the velocity of ocean currents in the mixing layer of the water column (where oil and water mix together)
* is the wind-driven shear stress
* f is the oil-water friction coefficient
* E is the relative difference in densities between the oil and water
* R is the rate of spill propagation
Mackay's model predicts an increasing dispersion rate, as the slick becomes thinner in one dimension. The model predicts that thin slicks will disperse faster than thick slicks for several reasons. Thin slicks are less effective at dampening waves and other sources of turbidity. Additionally, droplets formed upon dispersion are expected to be smaller in a thin slick and thus easier to disperse in water.
The model also includes:
* An expression for the diameter of the oil drop
* Temperature dependence of oil movement
* An expression for the resurfacing of oil
* Calibrations based on data from experimental spills
The model is lacking in several areas: it does not account for evaporation, the topography of the ocean floor or the geography of the spill zone.
Johansens model is more complex than Mackays model. It considers particles to be in one of three states: at the surface, entrained in the water column or evaporated. The empirically based model uses probabilistic variables to determine where the dispersant will move and where it will go after it breaks up oil slicks. The drift of each particle is determined by the state of that particle; this means that a particle in the vapor state will travel much further than a particle on the surface (or under the surface) of the ocean. This model improves on Mackay's model in several key areas, including terms for:
* Probability of entrainment – depends on wind
* Probability of resurfacing – depends on density, droplet size, time submerged and wind
* Probability of evaporation – matched with empirical data
Oil dispersants are modeled by Johansen using a different set of entrainment and resurfacing parameters for treated versus untreated oil. This allows areas of the oil slick to be modeled differently, to better understand how oil spreads along the water's surface. | 2 | Environmental Chemistry |
In cellular biology, inclusions are diverse intracellular non-living substances (ergastic substances) that are not bound by membranes. Inclusions are stored nutrients/deutoplasmic substances, secretory products, and pigment granules. Examples of inclusions are glycogen granules in the liver and muscle cells, lipid droplets in fat cells, pigment granules in certain cells of skin and hair, and crystals of various types. Cytoplasmic inclusions are an example of a biomolecular condensate arising by liquid-solid, liquid-gel or liquid-liquid phase separation.
These structures were first observed by O. F. Müller in 1786. | 1 | Biochemistry |
The compound crystallized in a monoclinic crystal structure. The space group is P2/n with four molecules in the unit cell. From the crystallographic data, a density of 2.365 g·cm was deduced. | 0 | Organic Chemistry |
Gitelson (1999) states, "The ratio between chlorophyll fluorescence at 735 nm and the wavelength range 700nm to 710 nm, F735/F700 was found to be linearly proportional to the chlorophyll content (with determination coefficient, r2, more than 0.95) and thus this ratio can be used as a precise indicator of chlorophyll content in plant leaves." | 5 | Photochemistry |
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases in the mixture (Dalton's Law).
The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules. Gases dissolve, diffuse, and react according to their partial pressures but not according to their concentrations in gas mixtures or liquids. This general property of gases is also true in chemical reactions of gases in biology. For example, the necessary amount of oxygen for human respiration, and the amount that is toxic, is set by the partial pressure of oxygen alone. This is true across a very wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood; consequently, mixture ratios, like that of breathable 20% oxygen and 80% Nitrogen, are determined by volume instead of by weight or mass. Furthermore, the partial pressures of oxygen and carbon dioxide are important parameters in tests of arterial blood gases. That said, these pressures can also be measured in, for example, cerebrospinal fluid. | 7 | Physical Chemistry |
One example of a binary chemical weapon is the United States Army M687. In the M687, methylphosphonyl difluoride (military name: DF, a Schedule 1 chemical) and a mixture of two agents are held in chambers within the munition, separated by a partition. When the weapon is fired, acceleration causes the partition to break, and the precursors are mixed by the rotation of the munition in flight, producing sarin nerve agent.
The Soviet Union and later Russian Federation experimented with binary munitions capable of mixing and distributing two agents that would work together in worsening the weapon's effects, an example of which would be the combination of nerve agents with blister agents.
The director of a non-proliferation research program of the Middlebury Institute of International Studies at Monterey has stated that the assassination of Kim Jong-nam due to poisoning with VX was likely carried out with a binary version of the agent, since VX fumes would otherwise have killed the suspected attackers. | 1 | Biochemistry |
Inflammatory bowel diseases (Crohn´s disease and ulcerative colitis) have been associated with mitochondrial dysfunction in the intestinal epithelium. In mouse models of intestinal inflammation and in IBD patients, signs of UPR -activation have been demonstrated. In particular, mitochondrial dysfunction and UPR -activation have been linked to intestinal stemness and Paneth cell (dys-)function. | 1 | Biochemistry |
Alkyl amines characteristically feature tetrahedral nitrogen centers. C-N-C and C-N-H angles approach the idealized angle of 109°. C-N distances are slightly shorter than C-C distances. The energy barrier for the nitrogen inversion of the stereocenter is about 7 kcal/mol for a trialkylamine. The interconversion has been compared to the inversion of an open umbrella into a strong wind.
Amines of the type NHRR and NRR′R″ are chiral: the nitrogen center bears four substituents counting the lone pair. Because of the low barrier to inversion, amines of the type NHRR cannot be obtained in optical purity. For chiral tertiary amines, NRR′R″ can only be resolved when the R, R, and R″ groups are constrained in cyclic structures such as N'-substituted aziridines (quaternary ammonium salts are resolvable). | 0 | Organic Chemistry |
Oligomer redox-species RFB have been proposed to reduce the crossover of the electroactive species, while using low cost membranes. Such redox-active oligomers are known as redoxymers. One system uses organic polymers and a saline solution with a cellulose membrane. The prototype underwent 10,000 charging cycles while retaining substantial capacity. The energy density was 10 Wh/L. Current density reached 100 milliamperes/cm.
Another oligomer RFB employs viologen and TEMPO redoxymers in combination with low-cost dialysis membranes. Functionalized macromolecules (similar to acrylic glass or Styrofoam) dissolved in water are the active electrode material. The size-selective nanoporous membrane works like a strainer and is produced much more easily and at lower cost than conventional ion-selective membranes. It retains the big "spaghetti"-like polymer molecules, while allowing small counterions to pass. The concept may solve the high cost of traditional Nafion membrane, but the design and synthesis of redox active polymer with high water solubility is not trivial. So far, RFBs with oligomer redox-species have not demonstrated competitive area-specific power. It is not clear whether low operating current density is an intrinsic feature of large redox-molecules or not. | 7 | Physical Chemistry |
Cryoprotectants are also used to preserve foods. These compounds are typically sugars that are inexpensive and do not pose any toxicity concerns. For example, many (raw) frozen chicken products contain a sucrose and sodium phosphates solution in water. | 1 | Biochemistry |
Due to low emission rate experiments should be performed in ultrahigh vacuum (UHV). In some studies the materials were previously doped with tritium. MSGE rate then was measured by radioactivity outcome from the material under applied mechanical stress. | 7 | Physical Chemistry |
HFMs are commonly produced using artificial polymers. The specific production methods involved are heavily dependent on the type of polymer used as well as its molecular weight. HFM production, commonly referred to as "spinning", can be divided into four general types:
* Melt Spinning, in which a thermoplastic polymer is melted and extruded through a spinneret into air and subsequently cooled.
* Dry Spinning, in which a polymer is dissolved in an appropriate solvent and extruded through a spinneret into air.
* Dry-Jet Wet Spinning, in which a polymer is dissolved in an appropriate solvent and extruded into air and a subsequent coagulant (usually water).
* Wet spinning, in which a polymer is dissolved and extruded directly into a coagulant (usually water).
Common to each of these methods is the use of a spinneret, a device containing a needle through which solvent is extruded and an annulus through which a polymer solution is extruded. As the polymer is extruded through the annulus of the spinneret, it retains a hollow cylindrical shape. As the polymer exits the spinneret, it solidifies into a membrane through a process known as phase inversion. The properties of the membrane -such as average pore diameter and membrane thickness- can be finely tuned by changing the dimensions of the spinneret, temperature and composition of "dope" (polymer) and "bore" (solvent) solutions, length of air gap (for dry-jet wet spinning), temperature and composition of the coagulant, as well as the speed at which produced fiber is collected by a motorized spool. Extrusion of the polymer and solvent through the spinneret can be accomplished either through the use of gas-extrusion or a metered pump. Some of the polymers most commonly used for fabricating HFMs include cellulose acetate, polysulfone, polyethersulfone, and polyvinylidene fluoride. | 7 | Physical Chemistry |
ANCAs were originally described in Davies et al. in 1982 in segmental necrotising glomerulonephritis. The Second International ANCA Workshop, held in The Netherlands in May 1989, fixed the nomenclature on perinuclear vs. cytoplasmic patterns, and the antigens MPO and PR3 were discovered in 1988 and 1989, respectively. International ANCA Workshops have been carried out every two years. | 1 | Biochemistry |
The Wolf effect (sometimes Wolf shift) is a frequency shift in the electromagnetic spectrum.
The phenomenon occurs in several closely related phenomena in radiation physics, with analogous effects occurring in the scattering of light. It was first predicted by Emil Wolf in 1987 and subsequently confirmed in the laboratory in acoustic sources by Mark F. Bocko, David H. Douglass, and Robert S. Knox, and a year later in optic sources by Dean Faklis and George Morris in 1988. | 7 | Physical Chemistry |
Bacteriophage derived proteins are used for detection and removal of bacteria and bacterial components (especially endotoxin contaminations) in pharmaceutical and biological products, human diagnostics, food, and decolonization of bacteria causing nosocomial infections (e.g. MRSA).
Protein modifications allow the biotechnological adaption to specific requirements. | 1 | Biochemistry |
Binding sites can be characterized also by their structural features. Single-chain sites (of “monodesmic” ligands, μόνος: single, δεσμός: binding) are formed by a single protein chain, while multi-chain sites (of "polydesmic” ligands, πολοί: many) are frequent in protein complexes, and are formed by ligands that bind more than one protein chain, typically in or near protein interfaces. Recent research shows that binding site structure has profound consequences for the biology of protein complexes (evolution of function, allostery). | 1 | Biochemistry |
After her postdoctoral research, she joined Indiana University, where she became an associate professor. She moved to the University of Maryland School of Pharmacy in 2016.
In her research, Jones focusses on structural proteomics, having developed fast photochemical oxidation of proteins (FPOP) which uses an excimer laser for photolysis, which generates hydroxyl radicals. Hydroxyl radicals go on to oxidise the side chains of amino acids and provide solvent accessibility of proteins within a cell. FPOP can provide information on the sites of ligand binding, protein interaction and protein conformational changes in vivo. More recently, her group has extended the platform with a no-flow platform for high-throughput in-cell measurements.
In 2019, she received the Biophysical Society's Junior Faculty Award.
Jones also works on science outreach and improving representation in the sciences. She is a mentor in the UMD CURE Scholars Program and a member of the American Society for Mass Spectrometry Diversity and Outreach Working Group. Jones is also co-director of the Initiative to Maximize Student Development (IMSD) Meyerhoff Graduate Fellowship Program, a program for increasing representation of minority students in STEM.
In 2021, Jones was in the news for turning down a faculty position at the University of North Carolina Chapel Hill in protest of controversy regarding the tenure status of journalist Nikole Hannah-Jones. | 1 | Biochemistry |
Mixed-function oxidase is the name of a family of oxidase enzymes that catalyze a reaction in which each of the two atoms of oxygen in O is used for a different function in the reaction.
Oxidase is a general name for enzymes that catalyze oxidations in which molecular oxygen is the electron acceptor but oxygen atoms do not appear in the oxidized product. Often, oxygen is reduced to either water (cytochrome oxidase of the mitochondrial electron transfer chain) or hydrogen peroxide (dehydrogenation of fatty acyl-CoA in peroxisomes). Most of the oxidases are flavoproteins.
The name "mixed-function oxidase" indicates that the enzyme oxidizes two different substrates simultaneously. Desaturation of fatty acyl-CoA in vertebrates is an example of the mixed-function oxidase reaction. In the process, saturated fatty acyl-CoA and NADPH are oxidized by molecular oxygen (O) to produce monounsaturated fatty acyl-CoA, NADP and 2 molecules of water. | 1 | Biochemistry |
Biosynthesis occurs in most human tissue. There are three major steps:
# Creation of the benzoquinone structure (using phenylalanine or tyrosine, via 4-hydroxybenzoate)
# Creation of the isoprene side chain (using acetyl-CoA)
# The joining or condensation of the above two structures
The initial two reactions occur in mitochondria, the endoplasmic reticulum, and peroxisomes, indicating multiple sites of synthesis in animal cells.
An important enzyme in this pathway is HMG-CoA reductase, usually a target for intervention in cardiovascular complications. The "statin" family of cholesterol-reducing medications inhibits HMG-CoA reductase. One possible side effect of statins is decreased production of CoQ, which may be connected to the development of myopathy and rhabdomyolysis. However, the role statins play in CoQ deficiency is controversial. Although statins reduce blood levels of CoQ, studies on the effects of muscle levels of CoQ are yet to come. CoQ supplementation also does not reduce side effects of statin medications.
Genes involved include PDSS1, PDSS2, COQ2, and ADCK3 (COQ8, CABC1).
Organisms other than humans produce the benzoquinone and isoprene structures from somewhat different source chemicals. For example, the bacteria E. coli produces the former from chorismate and the latter from a non-mevalonate source. The common yeast S. cerevisiae, however, derives the former from either chorismate or tyrosine and the latter from mevalonate. Most organisms share the common 4-hydroxybenzoate intermediate, yet again uses different steps to arrive at the "Q" structure. | 1 | Biochemistry |
The energy required to detach an electron in its lowest energy state from an atom or molecule of a gas with less net electric charge is called the ionization potential, or ionization energy. The nth ionization energy of an atom is the energy required to detach its nth electron after the first electrons have already been detached.
Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron in its outermost shell, so in ionized form it is commonly found with one lost electron, as . On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as . Caesium has the lowest measured ionization energy of all the elements and helium has the greatest. In general, the ionization energy of metals is much lower than the ionization energy of nonmetals, which is why, in general, metals will lose electrons to form positively charged ions and nonmetals will gain electrons to form negatively charged ions. | 7 | Physical Chemistry |
The Cephalodiscidae mitochondrial code (translation table 33) is a genetic code used by the mitochondrial genome of Cephalodiscidae (Pterobranchia). The Pterobranchia are one of the two groups in the Hemichordata which together with the Echinodermata and Chordata form the major clades of deuterostomes.
Code 33 is very similar to the mitochondrial code 24 for the Pterobranchia, which also belong to the Hemichordata, except that it uses UAA for tyrosine rather than as a stop codon.
This code shares with many other mitochondrial codes the reassignment of the UGA STOP to tryptophan, and AGG and AGA to an amino acid other than arginine. However, the assignment of AGG to lysine in pterobranchian mitogenomes is not found elsewhere in deuterostome mitochondria but it occurs in some taxa of Arthropoda. | 1 | Biochemistry |
A lateral flow test (LFT), is an assay also known as a lateral flow device (LFD), lateral flow immunochromatographic assay, or rapid test. It is a simple device intended to detect the presence of a target substance in a liquid sample without the need for specialized and costly equipment. LFTs are widely used in medical diagnostics in the home, at the point of care, and in the laboratory. For instance, the home pregnancy test is an LFT that detects a specific hormone. These tests are simple and economical and generally show results in around five to thirty minutes. Many lab-based applications increase the sensitivity of simple LFTs by employing additional dedicated equipment. Because the target substance is often a biological antigen, many lateral flow tests are rapid antigen tests (RAT or ART).
LFTs operate on the same principles of affinity chromatography as the enzyme-linked immunosorbent assays (ELISA). In essence, these tests run the liquid sample along the surface of a pad with reactive molecules that show a visual positive or negative result. The pads are based on a series of capillary beds, such as pieces of porous paper, microstructured polymer, or sintered polymer. Each of these pads has the capacity to transport fluid (e.g., urine, blood, saliva) spontaneously.
The sample pad acts as a sponge and holds an excess of sample fluid. Once soaked, the fluid flows to the second conjugate pad in which the manufacturer has stored freeze dried bio-active particles called conjugates (see below) in a salt–sugar matrix. The conjugate pad contains all the reagents required for an optimized chemical reaction between the target molecule (e.g., an antigen) and its chemical partner (e.g., antibody) that has been immobilized on the particle's surface. This marks target particles as they pass through the pad and continue across to the test and control lines. The test line shows a signal, often a color as in pregnancy tests. The control line contains affinity ligands which show whether the sample has flowed through and the bio-molecules in the conjugate pad are active. After passing these reaction zones, the fluid enters the final porous material, the wick, that simply acts as a waste container.
LFTs can operate as either competitive or sandwich assays. | 1 | Biochemistry |
Less studied than above-ground interactions, but proving to be increasingly important, are the below-ground interactions that influence plant defense. There is a complex network of signal transduction pathways involved in plant responses to stimuli, and soil microbes can influence these responses. Certain soil microbes aid plant growth, producing increased tolerance to various environmental stressors, and can protect their host plants from many different pathogens by inducing systemic resistance. Organisms in above- and below-ground environments can interact indirectly through plants. Many studies have shown both the positive and negative effects that one organism in one environment can have on other organisms in the same or opposite environment, with the plant acting as the intermediary.
The colonization of plant roots with mycorhizae typically results in a mutualistic relationship between the plant and the fungus, inducing a number of changes in the plant. Such colonization has a mixed impact on herbivores; insects with different feeding methods are affected differently, some positively and others negatively. The mycorhizal species involved also matters. One common species, Rhizophagus irregularis, has been observed to have a negative effect on the feeding success of chewing herbivores, whereas other species studied have positive effects.
The roots of some maize plants produce a defense chemical when roots are damaged by leaf beetle larvae; this chemical attracts the entomopathogenic nematode species Heterorhabditis megidis. Only certain maize varieties produce this chemical; plants that release the chemical see up to five times as much parasitization of leaf beetle larvae as those that do not. Incorporating these varieties or their genes into commercial maize production could increase the efficacy of nematode treatments.
Further studies suggest that the plant-emitted chemicals act as the primary source of attractant to the nematodes. Herbivores are believed to have evolved to evade detection on the part of the nematodes, whereas the plants have evolved to release highly attractive chemical signals. A high degree of specificity is involved; species that make up these tritrophic interactions have evolved with one another over a long period of time and as a result have close interrelationships.
Microorganisms can also influence tritrophic interactions. The bacterium Klebsiella aerogenes produces the volatile 2,3-butanediol, which modulates interactions between plants, pathogens, and insects. When maize plants are grown in a soil culture containing the bacterium or the plants are inoculated with the bacterium, the maize is more resistant to the fungus Setosphaeria turcica. The bacterium does not deter insect herbivory; it actually increases weight gain and leaf consumption in the caterpillar Spodoptera littoralis. However, the parasitic wasp Cotesia marginiventris is attracted more readily to maize plants grown in soil cultures containing either the volatile-producing bacterium or pure 2,3-butanediol. | 1 | Biochemistry |
It may be necessary to repair a concrete structure following damage (e.g. due to age, chemical attack, fire, impact, movement or reinforcement corrosion). Strengthening may be necessary if the structure is weakened (e.g. due to design or construction errors, excessive loading, or because of a change of use). | 8 | Metallurgy |
The suffix –ol is used in organic chemistry principally to form names of organic compounds containing the hydroxyl (–OH) group, mainly alcohols. The suffix was extracted from the word alcohol.
The suffix also appears in some trivial names with reference to oils (from Latin oleum, oil). Examples of this sense of the suffix include phenol, eugenol, urushiol, and menthol. | 0 | Organic Chemistry |
Reverse electron flow (also known as reverse electron transport) is a mechanism in microbial metabolism. Chemolithotrophs using an electron donor with a higher redox potential than NAD(P)/NAD(P)H, such as nitrite or sulfur compounds, must use energy to reduce NAD(P). This energy is supplied by consuming proton motive force to drive electrons in a reverse direction through an electron transport chain and is thus the reverse process as forward electron transport. In some cases, the energy consumed in reverse electron transport is five times greater than energy gained from the forward process. Autotrophs can use this process to supply reducing power for inorganic carbon fixation.
Reverse electron transfer (RET) is the process that can occur in respiring mitochondria, when a small fraction of electrons from reduced ubiquinol is driven upstream by the membrane potential towards mitochondrial complex I. This results in reduction of oxidized pyridine nucleotide (NAD or NADP). This is a reversal of the exergonic reaction of forward electron transfer in the mitochondrial complex I when electrons travel from NADH to ubiquinone. | 1 | Biochemistry |
Isometries requiring an odd number of mirrors — reflection and glide reflection — always reverse left and right. The even isometries — identity, rotation, and translation — never do; they correspond to rigid motions, and form a normal subgroup of the full Euclidean group of isometries. Neither the full group nor the even subgroup are abelian; for example, reversing the order of composition of two parallel mirrors reverses the direction of the translation they produce.
Since the even subgroup is normal, it is the kernel of a homomorphism to a quotient group, where the quotient is isomorphic to a group consisting of a reflection and the identity. However the full group is not a direct product, but only a semidirect product, of the even subgroup and the quotient group. | 3 | Analytical Chemistry |
*TXN2 NM_012473
*TXNDC11 NM_015914
*TXNDC12 NM_015913
*TXNDC15 NM_024715
*TXNDC17 NM_032731
*TXNDC9 NM_005783
*TXNL1 NM_004786
*TXNL4A NM_006701
*TXNL4B NM_017853
*TXNRD1 NM_003330 | 1 | Biochemistry |
François Charles Léon Moureu (19 April 1863, in Mourenx – 13 June 1929, in Biarritz) was a French organic chemist and pharmacist. In 1902 Charles Moureu published , translated into English as Fundamental principles of organic chemistry (1921).
During World War I, Charles Moureu was vice-chairman of France's Committee for Gas Warfare. In this role, he established 16 chemistry laboratories in Paris, supervising their work until 1918. Moureu also became chairman of the Committee of National Defence when it was established in 1925, leading it until his death in 1929.
During the war, he researched acrolein and sulfur mustard gas, working with Charles Dufraisse. This work led them to pioneering research into autoxidation and antioxidants.
Moureu supported initiatives for international cooperation and standardization among chemists. He was one of the vice-presidents of the (SCF) in 1910, and the founding President of the International Union of Pure and Applied Chemistry (IUPAC) from 1920 to 1922. | 0 | Organic Chemistry |
2DPs are expected to be superb membrane materials because of their defined pore sizes. Furthermore, they can serve as ultrasensitive pressure sensors, as precisely defined catalyst supports, for surface coatings and patterning, as ultrathin support for cryo-TEM, and many other applications.
Since 2D polymers provide an availability of large surface area and uniformity in sheets, they also found useful applications in areas such as selective gas adsorption and separation. Metal organic frameworks have become popular recently due to the variability of structures and topology which provide tunable pore structures and electronic properties. There are also ongoing methods for creation of nanocrystals of MOFs and their incorporation into nanodevices. Additionally, metal-organic surfaces have been synthesized with cobalt dithionlene catalysts for efficient hydrogen production through reduction of water as an important strategy for fields of renewable energy.
The fabrication of 2D organic frameworks, have also synthesized two-dimensional, porous covalent organic frameworks to be used as storage media for hydrogen, methane and carbon dioxide in clean energy applications. | 7 | Physical Chemistry |
The "tuck-in" process is related to ortho-metalation in the sense that it is an intramolecular cyclometalation. Tuck-in complexes derived from Cp* ligands are derivatives of tetramethylfulvene, sometimes abbreviated MeFv. A variety of complexes are known for MeFv and related ligands. In these complexes, the Fv can serve as a 4-electron or as a 6-electron ligand. | 0 | Organic Chemistry |
Soda ash [NaCO] can be present in natural water from the weathering of basalt which is an igneous rock. Lime [Ca(OH)] can be present in natural water when rain water comes in contact with calcined minerals such as ash produced from the burning of calcareous coal or lignite in boilers. Anthropogenic use of soda ash also finally adds to the RSC of the river water.
Where the river water and ground water are repeatedly used in the extensively irrigated river basins, the river water available in lower reaches is often rendered not useful in agriculture due to high RSC index or alkalinity. The salinity of water need not be high. | 9 | Geochemistry |
The planetary equilibrium temperature is a theoretical temperature that a planet would be if it was in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is irrelevant, as the equilibrium temperature is calculated purely from a balance with incident stellar energy.
Other authors use different names for this concept, such as equivalent blackbody temperature of a planet. The effective radiation emission temperature is a related concept, but focuses on the actual power radiated rather than on the power being received, and so may have a different value if the planet has an internal energy source or when the planet is not in radiative equilibrium.
Planetary equilibrium temperature differs from the global mean temperature and surface air temperature, which are measured observationally by satellites or surface-based instruments, and may be warmer than the equilibrium temperature due to the greenhouse effect. | 7 | Physical Chemistry |
Chemical thermodynamics is the study of the interrelation of energy with chemical reactions or with a physical change of state within the confines of the laws of thermodynamics. The primary objective of chemical thermodynamics is determining the spontaneity of a given transformation. | 7 | Physical Chemistry |
There are three types of sweat glands: eccrine, apocrine, and apoeccrine. Apocrine glands are primarily responsible for body malodor and, along with apoeccrine glands, are mostly expressed in the axillary (underarm) regions, whereas eccrine glands are distributed throughout virtually all of the rest of the skin in the body, although they are also particularly expressed in the axillary regions, and contribute to malodor to a relatively minor extent. Sebaceous glands, another type of secretory gland, are not sweat glands but instead secrete sebum (an oily substance), and may also contribute to body odor to some degree.
The main odorous compounds that contribute to axillary odor include:
# Unsaturated or hydroxylated branched fatty acids, with the key ones being (E)-3-methyl-2-hexenoic acid (3M2H) and 3-hydroxy-3-methylhexanoic acid (HMHA)
# Sulfanylalkanols, particularly 3-methyl-3-sulfanylhexan-1-ol (3M3SH)
# Odoriferous androstane steroids, namely the pheromones androstenone (5α-androst-16-en-3-one) and androstenol (5α-androst-16-en-3α-ol)
These malodorous compounds are formed from non-odoriferous precursors that are secreted from apocrine glands and converted by various enzymes expressed in skin surface bacteria. The specific skin surface bacteria responsible are mainly Staphylococcus and Corynebacterium species.
The androstane steroids dehydroepiandrosterone sulfate (DHEA-S) and androsterone sulfate have been detected in an extract of axillary hairs together with high concentrations of cholesterol. Apocrine sweat contains relatively high amounts of androgens, for instance dehydroepiandrosterone (DHEA), androsterone, and testosterone, and the androgen receptor (AR), the biological target of androgens, is strongly expressed in the secretory cells of apocrine glands. In addition, 5α-reductase type I, an enzyme which converts testosterone into the more potent androgen dihydrotestosterone (DHT), has been found to be highly expressed in the apocrine glands of adolescents, and DHT has been found to specifically contribute to malodor as well. Starting at puberty, males have higher levels of androgens than do females and produce comparatively more axillary malodor. As such, it has been proposed that the higher axillary malodor seen in males is due to greater relative stimulation of axillary apocrine sweat glands by androgens. | 1 | Biochemistry |
In recent years, thermal physics has applied the definition of chemical potential to systems in particle physics and its associated processes. For example, in a quark–gluon plasma or other QCD matter, at every point in space there is a chemical potential for photons, a chemical potential for electrons, a chemical potential for baryon number, electric charge, and so forth.
In the case of photons, photons are bosons and can very easily and rapidly appear or disappear. Therefore, at thermodynamic equilibrium, the chemical potential of photons is in most physical situations always and everywhere zero. The reason is, if the chemical potential somewhere was higher than zero, photons would spontaneously disappear from that area until the chemical potential went back to zero; likewise, if the chemical potential somewhere was less than zero, photons would spontaneously appear until the chemical potential went back to zero. Since this process occurs extremely rapidly - at least, it occurs rapidly in the presence of dense charged matter or also in the walls of the textbook example for a photon gas of blackbody radiation - it is safe to assume that the photon chemical potential here is never different from zero. A physical situation where the chemical potential for photons can differ from zero are material-filled optical microcavities, with spacings between cavity mirrors in the wavelength regime. In such two-dimensional cases, photon gases with tuneable chemical potential, much reminiscent to gases of material particles, can be observed.
Electric charge is different because it is intrinsically conserved, i.e. it can be neither created nor destroyed. It can, however, diffuse. The "chemical potential of electric charge" controls this diffusion: Electric charge, like anything else, will tend to diffuse from areas of higher chemical potential to areas of lower chemical potential. Other conserved quantities like baryon number are the same. In fact, each conserved quantity is associated with a chemical potential and a corresponding tendency to diffuse to equalize it out.
In the case of electrons, the behaviour depends on temperature and context. At low temperatures, with no positrons present, electrons cannot be created or destroyed. Therefore, there is an electron chemical potential that might vary in space, causing diffusion. At very high temperatures, however, electrons and positrons can spontaneously appear out of the vacuum (pair production), so the chemical potential of electrons by themselves becomes a less useful quantity than the chemical potential of the conserved quantities like (electrons minus positrons).
The chemical potentials of bosons and fermions is related to the number of particles and the temperature by Bose–Einstein statistics and Fermi–Dirac statistics respectively. | 7 | Physical Chemistry |
Grain boundary sliding is a plastic deformation mechanism where crystals can slide past each other without friction and without creating significant voids as a result of diffusion. The deformation process associated with this mechanism is referred to as granular flow. The absence of voids results from solid-state diffusive mass transfer, locally enhanced crystal plastic deformation, or solution and precipitation of a grain boundary fluid. This mechanism operates at a low strain rate produced by neighbor switching. Grain boundary sliding is grain size- and temperature-dependent. It is favored by high temperatures and the presence of very fine-grained aggregates where diffusion paths are relatively short. Large strains operating in this mechanism do not result in the development of a lattice preferred orientation or any appreciable internal deformation of the grains, except at the grain boundary to accommodate the grain sliding; this process is called superplastic deformation. | 8 | Metallurgy |
In host–guest chemistry the bistable states of molecular switches differ in their affinity for guests. Many early examples of such systems are based on crown ether chemistry. The first switchable host is described in 1978 by Desvergne & Bouas-Laurent who create a crown ether via photochemical anthracene dimerization. Although not strictly speaking switchable the compound is able to take up cations after a photochemical trigger and exposure to acetonitrile gives back the open form.
In 1980 Yamashita et al. construct a crown ether already incorporating the anthracene units (an anthracenophane) and also study ion uptake vs photochemistry.
Also in 1980 Shinkai throws out the anthracene unit as photoantenna in favor of an azobenzene moiety and for the first time envisions the existence of molecules with an on-off switch. In this molecule light triggers a trans-cis isomerization of the azo group which results in ring expansion. Thus in the trans form the crown binds preferentially to ammonium, lithium and sodium ions while in the cis form the preference is for potassium and rubidium (both larger ions in same alkali metal group). In the dark the reverse isomerization takes place.
Shinkai employs this devices in actual ion transport mimicking the biochemical action of monensin and nigericin: in a biphasic system ions are taken up triggered by light in one phase and deposited in the other phase in absence of light. | 6 | Supramolecular Chemistry |
In chemistry, absorption is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter some bulk phase – liquid or solid material. This is a different process from adsorption, since molecules undergoing absorption are taken up by the volume, not by the surface (as in the case for adsorption).
A more common definition is that "Absorption is a chemical or physical phenomenon in which the molecules, atoms and ions of the substance getting absorbed enter into the bulk phase (gas, liquid or solid) of the material in which it is taken up."
A more general term is sorption, which covers absorption, adsorption, and ion exchange. Absorption is a condition in which something takes in another substance.
In many processes important in technology, the chemical absorption is used in place of the physical process, e.g., absorption of carbon dioxide by sodium hydroxide – such acid-base processes do not follow the Nernst partition law (see: solubility).
For some examples of this effect, see liquid-liquid extraction. It is possible to extract a solute from one liquid phase to another without a chemical reaction. Examples of such solutes are noble gases and osmium tetroxide.
The process of absorption means that a substance captures and transforms energy. The absorbent distributes the material it captures throughout whole and adsorbent only distributes it through the surface.
The process of gas or liquid which penetrate into the body of adsorbent is commonly known as absorption. | 7 | Physical Chemistry |
The deeper layers of the ocean are greatly unsaturated in CO and its dissolved forms, carbonic and bicarbonic acid, and their salts. At depths greater than 3 km, CO becomes liquefied and sinks to the seafloor due to it being higher density than the surrounding seawater. Mathematical models have shown that CO stored in deep sea sediments beyond 3 km could provide permanent geological storage even with large geomechanical perturbations. Deep ocean storage can present a potential sink for large amounts of anthropogenic CO. Other deep water carbon storage techniques currently being explored include, seaweed farming and algae, ocean fertilization, artificial upwelling, and basalt storage.
The deep blue carbon terminology has been used in passing as early as 2017. The Ocean Frontier Institute has made it a centrepiece of their participation at COP27. It is investing significant resources into deep blue carbon research. In terms of net-new-carbon sequestration deep blue carbon offers an estimated 10-20 times higher potential than coastal blue carbon to achieve net-zero goals. There is still a lack of data in this area along with financial, ecological and environmental concerns. Advancements in research and technical capabilities are raising international interest in this kind of storage. | 9 | Geochemistry |
Tentative evidence in Alzheimer's disease showed that lithium may slow progression. It has been studied for its potential use in the treatment of amyotrophic lateral sclerosis (ALS), but a study showed lithium had no effect on ALS outcomes. | 1 | Biochemistry |
TRC105 is an experimental antibody targeted at endoglin as an anti-angiogenesis treatment for soft-tissue sarcoma. | 1 | Biochemistry |
Early studies in Caenorhabditis elegans and Drosophila melanogaster saw large-scale, systematic loss of function (LOF) screens performed through saturation mutagenesis, demonstrating the potential of this approach to characterise genetic pathways and identify genes with unique and essential functions. The saturation mutagenesis technique was later applied in other organisms, for example zebrafish and mice.
Targeted approaches for gene knockdown emerged in the 1980s with techniques such as homologous recombination, trans-cleaving ribozymes, and antisense technologies.
By the year 2000, RNA interference (RNAi) technology had emerged as a fast, simple, and inexpensive technique for targeted gene knockdown, and was routinely being used to study in vivo gene function in C. elegans. Indeed, in the span of only a few years following its discovery by Fire et al. (1998), almost all of the ~19,000 genes in C. elegans had been analysed using RNAi-based knockdown.
The production of RNAi libraries facilitated the application of this technology on a genome-wide scale, and RNAi-based methods became the predominant approach for genome-wide knockdown screens.
Nevertheless, RNAi-based approaches to genome-wide knockdown screens have their limitations. For one, the high off-target effects cause issues with false-positive observations. Additionally, because RNAi reduces gene expression at the post-transcriptional level by targeting RNA, RNAi-based screens only result in partial and short-term suppression of genes. Whilst partial knockdown may be desirable in certain situations, a technology with improved targeting efficiency and fewer off-target effects was needed.
Since initial identification as a prokaryotic adaptive immune system, the bacterial type II clustered regularly interspaced short palindrome repeats (CRISPR)/Cas9 system has become a simple and efficient tool for generating targeted LOF mutations. It has been successfully applied to edit human genomes, and has started to displace RNAi as the dominant tool in mammalian studies. In the context of genome-wide knockout screens, recent studies have demonstrated that CRISPR/Cas9 screens are able to achieve highly efficient and complete protein depletion, and overcome the off-target issues seen with RNAi screens. In summary, the recent emergence of CRISPR-Cas9 has dramatically increased our ability to perform large-scale LOF screens. The versatility and programmability of Cas9, coupled with the low noise, high knockout efficiency and minimal off-target effects, have made CRISPR the platform of choice for many researchers engaging in gene targeting and editing. | 1 | Biochemistry |
A small scale study of 289 Japanese patients suggested a minor increased predisposition from an amino acid substitution of the 196 allele at exon 6. Genomic testing of 81 SLE patients and 207 healthy patients in a Japanese study showed 37% of SLE patients had a polymorphism on position 196 of exon 6 compared to 18.8% of healthy patients. The TNFR2 196R allele polymorphism suggests that even one 196R allele results in increased risk for SLE. | 1 | Biochemistry |
Within the chemical universe, the fine chemical industry is positioned between the commodity, their suppliers, and specialty chemical industries, their customers. Depending on the services offered, there are two types of fine chemical companies. The Fine Chemical Companies are active in industrial scale production, both of standard and exclusive products. If the latter prevails, they are referred to as Fine Chemical / Custom Manufacturing Organizations (CMOs). The main assets of the Contract Research Organizations (CROs) are their research laboratories. CRAMS; Contract Research and Manufacturing Organizations are hybrids (see section 4.2). | 0 | Organic Chemistry |
AIDS appears to involve a slow and progressive decline in levels of selenium in the body. Whether this decline in selenium levels is a direct result of the replication of HIV or related more generally to the overall malabsorption of nutrients by AIDS patients remains debated. Observational studies have found an association between decreased selenium levels and poorer outcomes in patients with HIV, though these studies were mostly done prior to the currently effective treatments with highly active antiretroviral therapy (HAART). Currently there is inadequate evidence to recommend routine selenium supplementation for HIV patients, and further research is recommended. | 1 | Biochemistry |
Dallol lies in the evaporitic plain of the Danakil Depression at the Afar Triangle, in the prolongation of the Erta Ale basaltic volcanic range. The intrusion of basaltic magma in the marine sedimentary sequence of Danakil resulted in the formation of a salt dome structure, where the hydrothermal system is hosted. The age of the hydrothermal system is unknown and the latest phreatic eruption that resulted in the formation of a diameter crater within the dome, took place in 1926. The wider area of Dallol is known as one of the driest and hottest places on the planet. It is also one of the lowest land points, lying below mean sea level. Other known hydrothermal features nearby Dallol are Gaet'Ale Pond and Black Lakes.
The hydrothermal springs of Dallol discharge anoxic, hyper-acidic (pH < 0), hyper-saline (almost 10 times more saline than seawater), high temperature (hotter than ) brines that contain more than 26 g/L of iron. The main gases emitted from the springs and fumaroles are carbon dioxide, hydrogen sulfide, nitrogen, sulfur dioxide; and traces of hydrogen, argon, and oxygen. Although several other hyper-acidic (pH < 2) volcanic systems exist, mainly found in crater lakes and hydrothermal sites, the pH values of Dallol decrease far below zero. The coexistence of such extreme physicochemical characteristics (pH, salinity, high temperature, lack of oxygen, etc.) render Dallol one of the very few ‘poly-extreme’ sites on Earth. This is why Dallol is a key system for astrobiological studies investigating the limits of life. Parts of the region are nearly sterile, except for a diverse array of "ultrasmall" archaea.
Dallol is highly dynamic; active springs go inactive and new springs emerge in new places in the range of days, and this is also reflected in the colors of the site that change with time, from white to green, lime, yellow, gold, orange, red, purple and ochre. In contrast to other hydrothermal systems known for their colorful pools (e.g. Grand Prismatic Spring), where the colors are generated by biological activity, the color palette of Dallol is produced by the inorganic oxidation of the abundant iron phases. Another fascinating feature of Dallol is the wide array of unusual mineral patterns, such as, salt-pillars, miniature geysers, water-lilies, flower-like crystals, egg-shaped crusts, and pearl-like spheres. The main mineral phases encountered at Dallol are halite, jarosite, hematite, akaganeite and other Fe-oxyhydroxides, gypsum, anhydrite, sylvite and carnallite. | 9 | Geochemistry |
A coarctate reaction is a concerted reaction whose transition state involves two rings, in which at least one atom undergoes the simultaneous making and breaking of two bonds. It is an uncommon reaction topology, compared with linear topology and pericyclic topology (itself subdivided into Hückel and Möbius topologies). The name is derived from the Latin , meaning . | 0 | Organic Chemistry |
Certain lachrymatory agents, most notably tear gas, are often used by police to force compliance. In some countries (e.g., Finland, Australia, and United States), another common substance is mace. The self-defense weapon form of mace is based on pepper spray which comes in small spray cans. Versions including CS are manufactured for police use. Xylyl bromide, CN and CS are the oldest of these agents. CS is the most widely used. CN has the most recorded toxicity.
Typical manufacturer warnings on tear gas cartridges state "Danger: Do not fire directly at person(s). Severe injury or death may result." Tear gas guns do not have a manual setting to adjust the range of fire. The only way to adjust the projectile's range is to aim towards the ground at the correct angle. Incorrect aim will send the capsules away from the targets, causing risk for non-targets instead. | 1 | Biochemistry |
hnRNP has been shown to regulate CD44, a cell-surface glycoprotein, through splicing mechanisms. CD44 is involved in cell-cell interactions and has roles in cell adhesion and migration. Splicing of CD44 and the functions of the resulting isoforms are different in breast cancer cells, and when knocked down, hnRNP reduced both cell viability and invasiveness. | 1 | Biochemistry |
One strategy to provide full 360° rotation of THz polarization of equal electric field magnitude at the sample is to generate a circular state of polarization, then select particular linear polarization states from the circularly polarized beam with a THz polarizer.
A circular polarization state may be generated by a quarter waveplate, however, common optical waveplates are typically designed for visible, near- and mid-infrared regions of the electromagnetic spectrum. A quarter waveplate designed for use in the THz frequency range consists of a right-angle silicon prism together with metal-coated planar mirrors as input/output. In particular, the silicon prism acts analogously to a Fresnel rhomb with a single total internal reflection on the longer face of the prism and is a passive broadband component that permits a wide frequency sweep during measurements. | 7 | Physical Chemistry |
With the advent of digitally based displays, some modern spectrum analyzers use analog-to-digital converters to sample spectrum amplitude after the VBW filter. Since displays have a discrete number of points, the frequency span measured is also digitised. Detectors are used in an attempt to adequately map the correct signal power to the appropriate frequency point on the display. There are in general three types of detectors: sample, peak, and average
*Sample detection – sample detection simply uses the midpoint of a given interval as the display point value. While this method does represent random noise well, it does not always capture all sinusoidal signals.
*Peak detection – peak detection uses the maximum measured point within a given interval as the display point value. This insures that the maximum sinusoid is measured within the interval; however, smaller sinusoids within the interval may not be measured. Also, peak detection does not give a good representation of random noise.
*Average detection – average detection uses all of the data points within the interval to consider the display point value. This is done by power (rms) averaging, voltage averaging, or log-power averaging. | 7 | Physical Chemistry |
Absorption of radiation by reactants of a reaction at equilibrium increases the rate of forward reaction without directly affecting the rate of the reverse reaction.
The rate of a photochemical reaction is proportional to the absorption cross section of the reactant with respect to the excitation source (σ), the quantum yield of reaction (Φ), and the intensity of the irradiation. In a reversible photochemical reaction between compounds A and B, there will therefore be a "forwards" reaction of at a rate proportional to and a "backwards" reaction of at a rate proportional to . The ratio of the rates of the forward and backwards reactions determines where the equilibrium lies, and thus the photostationary state is found at:
If (as is always the case to some extent) the compounds A and B have different absorption spectra, then there may exist wavelengths of light where σ is high and σ is low. Irradiation at these wavelengths will provide photostationary states that contain mostly B. Likewise, wavelengths that give photostationary states of predominantly A may exist. This is particularly likely in compounds such as some photochromics, where A and B have entirely different absorption bands. Compounds that may be readily switched in this way find utility in devices such as molecular switches and optical data storage. | 5 | Photochemistry |
While the secretion of glucocorticoids in response to stressful stimuli is an adaptive response necessary for an organism to respond appropriately to a stressor, persistent secretion may be harmful. The endocannabinoid system has been implicated in the habituation of the hypothalamic-pituitary-adrenal axis (HPA axis) to repeated exposure to restraint stress. Studies have demonstrated differential synthesis of anandamide and 2-AG during tonic stress. A decrease of anandamide was found along the axis that contributed to basal hypersecretion of corticosterone; in contrast, an increase of 2-AG was found in the amygdala after repeated stress, which was negatively correlated to magnitude of the corticosterone response. All effects were abolished by the CB antagonist AM251, supporting the conclusion that these effects were cannabinoid-receptor dependent. These findings show that anandamide and 2-AG divergently regulate the HPA axis response to stress: while habituation of the stress-induced HPA axis via 2-AG prevents excessive secretion of glucocorticoids to non-threatening stimuli, the increase of basal corticosterone secretion resulting from decreased anandamide allows for a facilitated response of the HPA axis to novel stimuli. | 1 | Biochemistry |
Traditional classification shows several theoretical and practical deficiencies. One of the most important is the fact that no perfectly isentropic fluid exists. Isentropic fluids have two extrema (ds/dT=0) on the saturation vapour curve. Practically, there are some fluids which are very close to this behaviour or at least in a certain temperature range, for example trichlorofluoromethane (CClF). Another problem is the extent of how dry or isentropic the fluid behaves, which has significant practical importance when designing for example an Organic Rankine Cycle layout and choosing proper expander.
A new kind of classification was proposed by G. Györke et al. to resolve the problems and deficiencies of the traditional three-class classification system. The new classification is also based on the shape of the saturation vapour curve of the fluid in temperature-entropy diagram similarly to the traditional one. The classification uses a characteristic-point based method to differentiate the fluids. The method defines three primary and two secondary characteristic points. The relative location of these points on the temperature-entropy saturation curve defines the categories. Every pure fluid has primary characteristic points A, C and Z:
* Primary point A and Z are the lowest temperature points on the saturation liquid and saturation vapour curve respectively. This temperature belongs to the melting point, which practically equals the triple point of the fluid. The choice of A and Z refers to the first and last point of the saturation curve visually.
* Primary point C refers to the critical point, which is an already well-defined thermodynamic property of the fluids.
The two secondary characteristic points, namely M and N are defined as local entropy extrema on the saturation vapour curve, more accurately, at those points, where with the decrease of the saturation temperature entropy stays constant: ds/dT=0. We can easily realise that considering traditional classification, wet-type fluids have only primary (A, C and Z), dry-type fluids have primary points and exactly one secondary point (M) and redefined isentropic-type fluids have both primary and secondary points (M and N) as well. See figure for better understanding.
The ascending order of entropy values of the characteristic points gives a useful tool to define categories. The mathematically possible number of orderings are 3! (if there are no secondary points), 4! (if only secondary point M exists) and 5! (if both secondary points exist), which makes it 150. There are some physical constraints including the existence of the secondary points decrease the number of possible categories to 8. The categories are to be named after the ascending order of the entropy of their characteristic points. Namely the possible 8 categories are ACZ, ACZM, AZCM, ANZCM, ANCZM, ANCMZ, ACNZM and ACNMZ. The categories (also called sequences) can be fitted into the traditional three-class classification, which makes the two classification system compatible. No working fluids have been found, which could be fitted into ACZM or ACNZM categories. Theoretical studies confirmed that these two categories may not even exist. Based on the database of NIST, the proved 6 sequences of the novel classification and their relation to the traditional one can be seen in the figure. | 7 | Physical Chemistry |
When a substance undergoes a phase transition (changes from one state of matter to another) it usually either takes up or releases energy. For example, when water evaporates, the increase in kinetic energy as the evaporating molecules escape the attractive forces of the liquid is reflected in a decrease in temperature. The energy required to induce the phase transition is taken from the internal thermal energy of the water, which cools the liquid to a lower temperature; hence evaporation is useful for cooling. See Enthalpy of vaporization. The reverse process, condensation, releases heat. The heat energy, or enthalpy, associated with a solid to liquid transition is the enthalpy of fusion and that associated with a solid to gas transition is the enthalpy of sublimation. | 7 | Physical Chemistry |
In the area of metal carbonyl clusters, a prototypical octahedral cluster is [FeC(CO)], which is obtained by heating iron pentacarbonyl with sodium. Some of the CO ligands are bridging and many are terminal. A carbide ligand resides at the center of the cluster. A variety of analogous compounds have been reported where some or all of the Fe centres are replaced by Ru, Mn and other metals.
Outside of carbonyl clusters, gold forms octahedral clusters. | 7 | Physical Chemistry |
Non-receptor tyrosine-protein kinase TYK2 is an enzyme that in humans is encoded by the TYK2 gene.
TYK2 was the first member of the JAK family that was described (the other members are JAK1, JAK2, and JAK3). It has been implicated in IFN-α, IL-6, IL-10 and IL-12 signaling. | 1 | Biochemistry |
In recent years, NAD has also been recognized as an extracellular signaling molecule involved in cell-to-cell communication. NAD is released from neurons in blood vessels, urinary bladder, large intestine, from neurosecretory cells, and from brain synaptosomes, and is proposed to be a novel neurotransmitter that transmits information from nerves to effector cells in smooth muscle organs. In plants, the extracellular nicotinamide adenine dinucleotide induces resistance to pathogen infection and the first extracellular NAD receptor has been identified. Further studies are needed to determine the underlying mechanisms of its extracellular actions and their importance for human health and life processes in other organisms. | 5 | Photochemistry |
Ramipril is a pro-drug. The molecule must be hydrolyzed by the esterase at the OCH2CH3 and form a carboxylate. This carboxylate then interacts with the positive Zn+2 to inhibit the ACE enzyme. The COOH helps orient it with the enzyme. Ramipril is similar in structure to another ACE Inhibitor, trandolapril, but it has a second cyclopentane ring instead of a cyclohexane ring. | 4 | Stereochemistry |
Bis(allyl)nickel is an organonickel compound with the formula Ni(η-CH). The molecule consists of two allyl ligands bound to nickel(II). It has inversion symmetry. It is a volatile yellow liquid at room temperature. | 0 | Organic Chemistry |
1916 - A.M. Butlerov Small Prize of the Russian Physics and Chemistry Society (for the research on the composition of oil of plant species of the same family)
1953 - Order of Lenin
1954 - Prize of the D.I. Mendeleev All-Union Chemical Society | 0 | Organic Chemistry |
For polystyrene the complete mechanism of photo-oxidation is still a matter of debate, as different pathways may operate concurrently and vary according to the wavelength of the incident light.
Regardless, there is agreement on the major steps.
Pure polystyrene should not be able to absorb light with a wavelength below ~280 nm and initiation is explained though photo-labile impurities (hydroperoxides) and charge transfer complexes, all of which are able to absorb normal sunlight. Charge-transfer complexes of oxygen and polystyrene phenyl groups absorb light to form singlet oxygen, which acts as a radical initiator. Carbonyl impurities in the polymer (c.f. acetophenone) also absorb light in the near ultraviolet range (300 to 400 nm), forming excited ketones able to abstract hydrogen atoms directly from the polymer. Hyroperoxide undergoes photolysis to form hydroxyl and alkoxyl radicals.
These initiation steps generate macroradicals at tertiary sites, as these are more stabilised. The propagation steps are essentially identical to those seen for polyolefins; with oxidation, hydrogen abstraction and photolysis leading to beta scission reactions and increasing numbers of radicals.
These steps account for the majority of chain-breaking, however in a minor pathway the hydroperoxide reacts directly with polymer to form a ketone group (acetophenone) and a terminal alkene without the formation of additional radicals.
Polystyrene is observed to yellow during photo-oxidation, which is attributed to the formation of polyenes from these terminal alkenes. | 5 | Photochemistry |
The South Turkmenistan Complex Archaeological Expedition (STACE), also called the South Turkmenistan Archaeological Inter-disciplinary Expedition of the Academy of Sciences of the Turkmen Soviet Socialist Republic (YuTAKE) was endorsed by the Turkmenistan Academy of Sciences. It was initially organized by the orientalist Mikhail Evgenievich Masson in 1946. The expedition had several excavations or "Brigades", based on sites and periods, and were spread over many years.
The Chalcolithic settlements of southern Turkmenistan, according to Masson, date to the late 5th millennium – early 3rd millennium BC, as assessed by carbon dating and paleomagnetic studies of the findings from the excavations carried out by STACE in the Altyndepe and Tekkendepe. The foothills of the Kopetdag mountains have revealed the earliest village cultures of Central Asia in the areas of Namazga-Tepe (more than 50 ha) and Altyndepe (26 ha), Ulug Depe (20 ha), Kara Depe (15 ha), and Geok-Syur (12 ha). In 1952, Boris Kuftin, established the basic Chalcolithics to Late Bronze Age sequence based on the excavations carried out at Namazga-Tepe (termed Namazga (NMG) I-VI).
However, the Chalcolithic period ended about 2700 BC due to natural factors of ecology, with the Geok-Syur oasis becoming desertified. This resulted in the migration of people to the ancient delta of the Tedzhen River. This also led to the Early Bronze Age Settlements at Khapuz-depe. | 8 | Metallurgy |
Anabolism operates with separate enzymes from catalysis, which undergo irreversible steps at some point in their pathways. This allows the cell to regulate the rate of production and prevent an infinite loop, also known as a futile cycle, from forming with catabolism.
The balance between anabolism and catabolism is sensitive to ADP and ATP, otherwise known as the energy charge of the cell. High amounts of ATP cause cells to favor the anabolic pathway and slow catabolic activity, while excess ADP slows anabolism and favors catabolism. These pathways are also regulated by circadian rhythms, with processes such as glycolysis fluctuating to match an animal's normal periods of activity throughout the day. | 1 | Biochemistry |
The total potential energy, , is the sum of the elastic strain energy, , stored in the deformed body and the potential energy, , associated to the applied forces:
This energy is at a stationary position when an infinitesimal variation from such position involves no change in energy:
The principle of minimum total potential energy may be derived as a special case of the virtual work principle for elastic systems subject to conservative forces.
The equality between external and internal virtual work (due to virtual displacements) is:
where
* = vector of displacements
* = vector of distributed forces acting on the part of the surface
* = vector of body forces
In the special case of elastic bodies, the right-hand-side of () can be taken to be the change, , of elastic strain energy due to infinitesimal variations of real displacements.
In addition, when the external forces are conservative forces, the left-hand-side of () can be seen as the change in the potential energy function of the forces. The function is defined as:
where the minus sign implies a loss of potential energy as the force is displaced in its direction. With these two subsidiary conditions, becomes:
This leads to () as desired. The variational form of () is often used as the basis for developing the finite element method in structural mechanics. | 7 | Physical Chemistry |
Radiation emitted from a surface can propagate in any direction from the surface. Irradiation can also be incident upon a surface from any direction. The amount of irradiation on a surface is therefore dependent on the relative orientation of both the emitter and the receiver. The parameter radiation intensity, is used to quantify how much radiation makes it from one surface to another.
Radiation intensity is often modeled using a spherical coordinate system. | 7 | Physical Chemistry |
Carbohydrate deficient transferrin increases in the blood with heavy ethanol consumption and can be monitored through laboratory testing.
Transferrin is an acute phase protein and is seen to decrease in inflammation, cancers, and certain diseases (in contrast to other acute phase proteins, e.g., C-reactive protein, which increase in case of acute inflammation). | 1 | Biochemistry |
A coactivator is a type of transcriptional coregulator that binds to an activator (a transcription factor) to increase the rate of transcription of a gene or set of genes. The activator contains a DNA binding domain that binds either to a DNA promoter site or a specific DNA regulatory sequence called an enhancer. Binding of the activator-coactivator complex increases the speed of transcription by recruiting general transcription machinery to the promoter, therefore increasing gene expression. The use of activators and coactivators allows for highly specific expression of certain genes depending on cell type and developmental stage.
Some coactivators also have histone acetyltransferase (HAT) activity. HATs form large multiprotein complexes that weaken the association of histones to DNA by acetylating the N-terminal histone tail. This provides more space for the transcription machinery to bind to the promoter, therefore increasing gene expression.
Activators are found in all living organisms, but coactivator proteins are typically only found in eukaryotes because they are more complex and require a more intricate mechanism for gene regulation. In eukaryotes, coactivators are usually proteins that are localized in the nucleus. | 1 | Biochemistry |
For most crystalline solid solutions, there is a variation of lattice parameters with the composition. If the lattice of such a solution is to remain coherent in the presence of a composition modulation, mechanical work has to be done to strain the rigid lattice structure. The maintenance of coherency thus affects the driving force for diffusion.
Consider a crystalline solid containing a one-dimensional composition modulation along the x-direction. We calculate the elastic strain energy for a cubic crystal by estimating the work required to deform a slice of material so that it can be added coherently to an existing slab of cross-sectional area. We will assume that the composition modulation is along the x' direction and, as indicated, a prime will be used to distinguish the reference axes from the standard axes of a cubic system (that is, along the <100>).
Let the lattice spacing in the plane of the slab be a and that of the undeformed slice a. If the slice is to be coherent after the addition of the slab, it must be subjected to a strain ε in the z and y directions which is given by:
In the first step, the slice is deformed hydrostatically in order to produce the required strains to the z and y directions. We use the linear compressibility of a cubic system 1 / ( c + 2 c ) where the c's are the elastic constants. The stresses required to produce a hydrostatic strain of δ are therefore given by:
The elastic work per unit volume is given by:
where the ε's are the strains. The work performed per unit volume of the slice during the first step is therefore given by:
In the second step, the sides of the slice parallel to the x direction are clamped and the stress in this direction is relaxed reversibly. Thus, ε = ε = 0. The result is that:
The net work performed on the slice in order to achieve coherency is given by:
or
The final step is to express c in terms of the constants referred to the standard axes. From the rotation of axes, we obtain the following:
where l, m, n are the direction cosines of the x' axis and, therefore the direction cosines of the composition modulation. Combining these, we obtain the following:
The existence of any shear strain has not been accounted for. Cahn considered this problem, and concluded that shear would be absent for modulations along <100>, <110>, <111> and that for other directions the effect of shear strains would be small. It then follows that the total elastic strain energy of a slab of cross-sectional area A is given by:
We next have to relate the strain δ to the composition variation. Let a be the lattice parameter of the unstrained solid of the average composition c. Using a Taylor series expansion about c yields the following:
in which
where the derivatives are evaluated at c. Thus, neglecting higher-order terms, we have:
Substituting, we obtain:
This simple result indicates that the strain energy of a composition modulation depends only on the amplitude and is independent of the wavelength. For a given amplitude, the strain energy W is proportional to Y. Consider a few special cases.
For an isotropic material:
so that:
This equation can also be written in terms of Youngs modulus E and Poissonss ratio υ using the standard relationships:
Substituting, we obtain the following:
For most metals, the left-hand side of this equation
is positive, so that the elastic energy will be a minimum for those directions that minimize the term: lm + mn + ln. By inspection, those are seen to be <100>. For this case:
the same as for an isotropic material. At least one metal (molybdenum) has an anisotropy of the opposite sign. In this case, the directions for minimum W will be those that maximize the directional cosine function. These directions are <111>, and
As we will see, the growth rate of the modulations will be a maximum in the directions that minimize Y. These directions, therefore, determine the morphology and structural characteristics of the decomposition in cubic solid solutions.
Rewriting the diffusion equation and including the term derived for the elastic energy yields the following:
or
which can alternatively be written in terms of the diffusion coefficient D as:
The simplest way of solving this equation is by using the method of Fourier transforms. | 7 | Physical Chemistry |
The precise function of the central domain has not been fully elucidated, but it is thought to be important in aiding catalysis. | 1 | Biochemistry |
9-Borabicyclo[3.3.1]nonane or 9-BBN is an organoborane compound. This colourless solid is used in organic chemistry as a hydroboration reagent. The compound exists as a hydride-bridged dimer, which easily cleaves in the presence of reducible substrates. 9-BBN is also known by its nickname banana borane. This is because rather than drawing out the full structure, chemists often simply draw a banana shape with the bridging boron. | 0 | Organic Chemistry |
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